OPTICS

Lesson notes - Grade 10 Optics - SNC2D1 - Ontario Curriculum 2009

Optics:

Direct light: Luminous objects that produce their own light
Indirect light:Non-luminous objects do not produce their own light, they reflect a luminous objects light

Incandescent light: When materials are heated light is produced this form of light is called incandescent light
- Sunlight
- Light bulb
- Molten metals
Phosphorescent light: Certain materials called phosphors gain energy from the surroundings and emit the extra energy that it has absorbed. The glow lasts for several hours.
- Luminous dials of certain watches and clocks are examples
Fluorescent light: Materials that emit light only during the time it receives energy from another source.
- Neon lamps
- Fluorescent light bulbs (These are four times more efficient as an incandescent bulb) It has an efficiency of 20%

Transparent: Materials that allow light to pass through, examples are water, clear plastic, glass etc.
Translucent: Materials that allow some light to pass through them, some light is scattered, examples are frosted glass, stained glass, shower curtain materials etc.
Opaque: Materials that do not allow light to pass through them, examples are wood, stone, rock etc.

Rectilinear propagation: Light appears to travel in straight lines through a uniform medium (uniform temperature and humidity if air is the medium)
- Proof that light travels in straight lines
  - Creation of shadows (umbra and penumbra)
  - Creation of upside images
- Types of shadows created
  - Umbra: When a point source light falls on an object and creates a shadow the region where light cannot reach is called the umbra and it is a distinct region
  - Penumbra: When a large source of light falls on an object it creates two types of shadow one that is distinct like the umbra and the second type of shadow that is a mixture - some light falls on this shadow, this region is called penumbra
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- Types of Images:
  - Real image: Images that can be projected on to a screen (Light comes directly from this image)
  - Virtual image: Images that cannot be projected on to a screen (Light does not come from this kind of image)
- Characteristics of an image:
  - Real or Virtual - Kind of image
  - Erect or Inverted - Attitude of the image
  - Enlarged, Same size or Diminished - Magnification

Ray: A directed straight line representing the path followed by the light
Beam: A bundle or rays
- Types of Beams
  - Parallel beams
  - Converging beams
  - Diverging beams
- Incident ray: Ray of light approaching the reflecting surface
- The ray of light leaving th reflecting surface
- Point of incidence: Point on the mirror where the incident ray strikes the reflecting surface
- Normal (N): A line perpendicular to the reflecting surface at the point of incidence
- Angle of incidence (i ) Angle between the incident ray and the normal
- Angle of reflection (r )Angle between the reflected ray and normal
Laws of reflection:
- The angle of incidence is equal to the angle of reflection
- The incident ray reflected ray and the normal all lie in the same plane

You tube clip laws of reflection

Concave - Converging mirror
Convex - Diverging mirror
- Related terminology
  - C - Center of curvature ( = 2f)
  - F - Principal focus (f = focal length)
  - V - Vertex
  - R - Radius of curvature
  - PA - Principal axis
Ray diagrams - Properties of reflected rays with respect to its path
- An incident ray parallel to the principal axis is always reflected through the focus
- An incident ray passing through F is always reflected parallel to the principal axis
- An incident ray passing through the center of curvature is always reflected back
- An incident ray striking the vertex is reflected based on the laws of reflection (angle of incidence = angle or reflection)